1. Field of the Invention
The present invention relates to a disc playback apparatus. The disc playback apparatus may be used in a personal computer, an audio system, or a navigation system, which reads data from a rotating disc storage medium.
2. Description of the Related Art
Optical discs are prevalent as readable storage media. The CD (Compact Disc), DVD (Digital Versatile Disc), and MD (Mini-Disc) are all examples of optical discs.
An optical disc has one or two signal recording surfaces on one side thereof. Each signal recording surface has holes referred to as xe2x80x9cpitsxe2x80x9d. There are several different lengths of pits. Pits of the different lengths are arrayed in combination in the longitudinal direction to form a track. In order to read data recorded in the disc, a computation is executed to determine the number of the tracks between the track corresponding to the instant position of an optical pickup and the track corresponding to an address storing the target data (this address will be referred to as xe2x80x9ctarget address,xe2x80x9d hereinafter). The optical pickup is moved in the radial direction of the disc across the tracks, while the number of the traversed tracks is counted, whereby the reading position of the optical pickup approaches the target address.
In recent years, there is a demand for shortening the time required for each seeking operation, i.e., an operation for moving the optical pickup reading position towards a target position, in order to achieve higher data reading speed. A conventional disc playback apparatus, however, produces a large error or difference between the target address and the address reached by the optical pickup in a single seeking cycle. Consequently, the seeking operation has to be repeated many times until the target address is reached, thus increasing the seeking time.
The seeking error, i.e. the difference between the reached address and the target address, is attributable to various factors. For instance, the error may be caused by variation in the precision of position control of the optical pickup, variation in the environment around the location where the disc playback apparatus is situated, change in the characteristics due to aging, error in the servo system that controls the radial traveling of the optical pickup, and so forth. These factors and, hence, the magnitude of the error vary according to the individual elements of the disc playback apparatus. Therefore, it has been difficult to apply a common countermeasure to all elements of the disc playback apparatus.
Increasing the optical pickup travel speed to shorten the seeking time also may lead to unstable seeking operation, because the variation in the factors according to the individual elements may cause a large deviation or error of the reached address from the target address. Further, however, it is not a common practice to make adjustments for each of the types of optical discs that may be used with the disc playback apparatus. Rather, a general adjustment, aiming at achieving a predetermined fixed optical pickup traveling speed is commonly preferred. In other words, it has been difficult to optimize the optical pickup traveling speed for each of the types of optical discs. This also makes it more difficult to shorten the seeking time.
Accordingly, it is an object of the present invention to provide a disc playback apparatus that shortens the seeking time while avoiding influence of variations of the elements of the playback apparatus.
In one embodiment of the present invention, a disc playback apparatus has an optical pickup, an optical pickup moving, a travel amount commanding means, travel amount error detecting means, and a travel amount correcting means. The optical pickup reads information stored in an optical disc. The optical pickup moving means causes the optical pickup to travel in a radial direction of the disc. The travel amount commanding means gives optical pickup travel amount command to the optical pickup moving means. The error detecting means detects a travel amount error in terms of the difference between the travel amount command formed by the travel amount commanding means and the amount actually traveled by the optical pickup by the operation of the optical pickup moving means. The travel amount correcting means corrects the value of the travel amount command so as to reduce the travel amount error. The travel amount command given to the optical pickup moving means to execute the seeking operation is determined in consideration of an error which is expected to occur upon actual traveling of the optical pickup. This permits the optical pickup to be efficiently moved to the position where the information to be read is stored, thus shortening the seeking time. The travel amount command is corrected based on the actual amount of error detected on each individual disc playback apparatus, so that each disc playback apparatus is enabled to perform the seeking operation with high accuracy, while compensating for variations in the individual apparatuses.
Preferably, the disc playback apparatus further has an error data storage means for storing the values of the travel amount error detected by the error detecting means, in relation to values of the travel amount command which are set at a predetermined pitch. This feature serves to reduce the size of the data to be stored in the error data storage means. In the error data storage means, the detected travel amount error values for each of the travel amount command values are stored and the travel amount values are set at a predetermined interval.
In particular, it is preferred that the error data storage means comprises a non-volatile memory. Use of a non-volatile memory such as EPROM permits the detected travel amount error data to be preserved even after the power to the disc playback apparatus is turned off. When the power is turned on again, correction of the travel amount command can be performed with a high degree of precision, by using the travel amount error data that had been accumulated before the power is turned off.
Preferably, the arrangement is such that the error data storage means stores the travel amount error in association with the direction of travel of the optical pickup caused by the optical pickup moving means, and that the travel amount correcting means performs the correction based on both the direction of travel and the travel amount error. The travel amount error produced when the optical pickup is being moved radially outward of the disc-type storage medium may differ from that produced when the optical pickup is being moved radially inward of the same, depending on the mechanical structure of the optical pickup moving means for causing the optical pickup to travel. When such a difference exists, the seeking precision can be enhanced to shorten the seeking time, by effecting the correction of the travel amount command while taking the direction of movement of the optical pickup into consideration.
The disc-type storage medium may have a plurality of layers providing signal recording surfaces. In such a case, the error data storage means is preferably arranged to store the travel amount error in association with the position of the layer of a signal recording surface, and the travel amount correcting means performs the correction based on both the position of the layer and the travel amount error. When a disc-type recording medium having a plurality of layers presenting signal recording surfaces is used, the travel amount error may have dependency on the position of the layer, because the intensity of the optical signal sensed by the optical pickup varies according to the position of the layer. In such a case, a further improvement in the seeking precision can be achieved by correcting the travel amount taking into account also the position of the layer which provides the signal recording surface carrying the signals to be read, thus contributing to the shortening of the seeking time.
Preferably, the apparatus further has an error data updating means for successively updating, in parallel with the operation for reproducing information read through the optical pickup, the content of the error data storage means based on the results of the detection performed by the error detecting means. The updating of the travel amount data error, which is performed in parallel with the ordinary reproducing operation, permits highly reliable correction of the travel amount command.
It is also preferred that the travel speed setting means which, when the travel amount error detected by the error detecting means exceeds a predetermined value, sets the travel speed of the optical pickup to a high speed if the position of the optical pickup after a travel is still short of a reading position corresponding to the travel amount command, and sets the travel speed to a low speed if the position of the optical pickup has overreached the reading position. By adjusting the travel speed of the optical pickup when the travel amount error is large, it is possible to avoid unstable seeking operation, thus contributing to shortening of the seeking time.
In accordance with another embodiment of the present invention, there is provided a disc playback apparatus comprising an optical pickup for optically reading information stored in an optical disc, an optical pickup moving means for causing the optical pickup to travel in a radial direction of the disc, a travel amount commanding means for giving optical pickup travel amount command to the optical pickup moving means, an error detecting means for detecting a travel amount error in terms of the difference between the travel amount command as the travel amount commanded by the travel amount commanding means and the amount actually traveled by the optical pickup by the operation of the optical pickup moving means, and a travel speed setting means which, when the travel amount error detected by the error detecting means exceeds a predetermined value, sets the travel speed of the optical pickup to a high speed if the position of the optical pickup after a travel is still short of a reading position corresponding to the travel amount command and to a low speed if the position of the optical pickup has overreached the reading position.
The tendency for the seeking operation becoming unstable is suppressed also by adjusting the traveling speed instead of the value of the travel amount command, thus achieving shortening of the seeking time.
In accordance with still another embodiment of the present invention, there is provided a seeking method for a disc playback apparatus having an optical pickup for optically reading information stored in an optical disc. The method comprises the acts of computing a travel amount command which commands the amount to be traveled by the optical pickup in a radial direction of the disc, detecting a travel amount error in terms of the difference between the travel amount command and the amount actually traveled by the optical pickup in accordance with the travel amount command, and correcting the value of the travel amount command so as to reduce the travel amount error.
In accordance with a further embodiment of the present invention, there is provided a seeking method for a disc playback apparatus having an optical pickup for optically reading information stored in an optical disc. The method comprises the acts of computing a travel amount command which commands the amount to be traveled by the optical pickup in a radial direction of the disc detecting a travel amount error in terms of the difference between the travel amount command and the amount actually traveled by the optical pickup in accordance with the travel amount command, storing the detected travel amount error in a memory, correcting the value of the travel amount command so as to reduce the travel amount error, and successively updating the content of the memory based on the results of the detection of the travel amount errors performed in every seeking operations.
In accordance with a still further embodiment of the present invention, there is provided a seeking method for a disc playback apparatus having an optical pickup for optically reading information stored in an optical disc. The method comprises the acts of commanding an amount to be traveled by the optical pickup in a radial direction of the disc, detecting a travel amount error in terms of the difference between the travel amount command and the amount actually traveled by the optical pickup in accordance with the travel amount command, and setting, when the travel amount error exceeds a predetermined value, the travel speed of the optical pickup to a high speed if the position of the optical pickup after a travel is still short of a reading position corresponding to the travel amount command, and to a low speed if the position of the optical pickup has overreached the reading position.
The above and other objects, features and advantages of the present invention will become clear from the following description of the preferred embodiments taken in conjunction with the accompanying drawings.